Arrow Speed Chronometer

Great link Brickie, I'll have to see if those guns are available over here.
Cheers (have a GA, and a sardine)
Del

How about just painting an arrow black then white then black.

Mount a little optical sensor on the bow, sensing the arrow and you should get a scope reading as it passes by?

I suppose it will still be accelerating though...

Or like the early years of lasers, they used gillette rasor blades to measure the power of their lasers.... The number of blades the laser punched a hole through was a measure of the power...

You could use panels of hardboard or something... calibrated with an arrow of known weight and pointy end!!?

So a bow could be calibrated in terms of the number of panels the arrow punched through....

**Hmmmm wonder if the NPL could make the measurement traceable**

I could wire a microswitch to the bow so that the string switches it at the end of the loose as the arrow leaves the string and another switch behind the target, and let the storage scope (or simple counter) do the rest. I s'pose that's simplest, just needs a know distance from bow to target, but it's a tad cumbersome.

The commercial ones have two sets of antennae, a bit like set top TV aerials which you shoot through.
Del

Put some RFID tag and sense with two sensors.

If the arrow has tails then it can simply interrupt a light on photocell- may be of a torch.

let it pass through two thin plastic membranes and pick up the vibtration a la spider (Do cats like spiders ?)

Aim at somebody and time the sound of string vs sound of the scream and correct for the distance (sound speed)

Aim it straight up. Measure time between release and touchdown. Solve for v. (Don't do this indoors)

.......and don't forget to wear a tin hat!!!

Difficult to use a stopwatch and shoot the bow. Not sure what terminal velocity of arrow is?
Ideally I want something I can use in the garage.
Del

I've seen clocks in pens why not stop watch in the arrow. Force of acceleration by the bow string turns it on shuts down on impact.

Place two well-inflated kiddie balloons (must be some shade of blue*) far apart at a known distance. Using a PC / laptop / portable audio recorder, start recording and let your arrow fly. Record the popping noises.

Using audio analysis software (available for freebie on the Internet) learn how far apart in time the pops are. Then by a process of applying the appropriate mathematics you should be able to work out the arrow speed.

*I just like blue. Besides, everyone knows that anything blue has greater accuracy.

Nice one.
But on a technical note, shouldn't the first balloon be red and the final one blue?
Not sure how accurate the distance between two wobbly baloons would be, but I could cage 'em somehow.

Del

You assume I can shoot an arrow accurately enough to pass a shadow over a photo sensor.
Maybe I can work it out from the apparent length of the arrow when filmed by my new camera, or distance between frames, dunno how accurate that would be?

Del

You wouldn't put the sensors behind a lens because you don't want to narrow the field-of-view too much. A 60°-90° FOV is standard for paintball chronos. You want to limit the FOV to this range, and no more, by placing the sensors at the bottom of shallow "wells." You may also wish to put a slightly darkened, but removable, filter over the sensors so that you won't saturate them with ambient light. Cheap sunglass lenses work great for this.

The photosensor (I'd use phototransistors myself, but you can experiment with small solar cells or photodiodes) outputs are differentiated because it is the change in the output signal that you're interested in - not the absolute value. The output of the differentiator will spike when the arrow passes overhead.

The arrows need not cast a shadow on the sensors necessarily. The sensors are just looking for a change in the background light, not a precision image as you'd get by using a lens. You need only shoot over the top of the thing, more or less. Unless your aim is downright abysmal (I seriously doubt it), you should be able to accurately measure your arrow speed in this way.

An arrow shaft shouldn't pose much of a problem, but it has a different optical cross-section than does a 0.68 caliber paint ball. This is where a gain adjustment (and threshold adjustment) comes in handy. Give yourself lots of gain, but also provide an external pot for trimming it down to a reasonable level. If you plan to build this thing, you might wish to use a cheap "instrumentation" amplifier chip in place of two, separate op-amps. The advantage is that an instrumentation amp rejects common-mode signals that might otherwise trigger your counter. With this kind of op-amp any change in the ambient light that affects both sensors simultaneously is rejected.

The advantage in this becomes apparent if you're going to do any night shooting - say on a well-lit range lit by stadium lights or whatever. Light sources supplied from the AC mains are going to flicker, even if you don't see the flicker unaided. For night shooting (calibrating before a meet, for example) you can put a small white-cloth "canopy" about 4 feet above the chrono and shine a lamp on it, or you can simply use the available light if it's bright enough.

I do a bit of night paintball and I calibrate my marker in this way before a match.

As for spacing, anything between 1.5 and 3 feet should work fine, though I'd probably opt for the former, but choose your counter's clock rate so that it gives you reasonable resolution over this distance. What is a typical arrow's speed? 200 fps? 300?

_{^{If you were a cute human girlie I might just do that.}}

170fps would be typical to good.
Yeah, but....how should I know I don't have a chrono
Del

BTW. Can't find Brickies toy radar gun in the UK and it only goes upto 100mph, mind can probably hack it to read more if I can find one.

If you want a resolution of, say, 1 fps, your counter will need to run somewhere around 20 kHz for a sensor spacing of 18". 32.768 kHz crystal oscillators are cheap, readily available and would give you a higher resolution than this.

Yup. GAs Mr E,
You've my brain fired up now, I've been doing sums but I came up with ~20kHz for 36" (strange that )

I reckon I can build an analogue front end like you say and interface it to one of my controller boards which has a nice 16 character 1 line display
I could even just run a software count and adjust the distance between the sensors for cal'.

I like the bounce light off a sheet for even illumination, mind you even light from British cloud cover is plentiful.

If I make one I'll post some pics.
Cheers
Del

_{<exits monitor left Farnell catalogue in paws, deep in thought>}

Yes, the arrow is thinner but the feathers at the end are much wider and longer.

Also you can always increase the clock frequency instead of the distance between the sensors.

Do you remember the BB Gun challenge question ? It was worded such that the target drops under gravity at the same time and rate as the projectile. Next, someone introduced the monkey gun, where you always hit the monkey (rigging it to drop at the right time with an electromagnet circuit). Yes?......rig something similar up, measure how far the monkey drops, then use one of those equation things. Maybe you could have some kind of make-on-break switch thing and shoot a tin foil strip to hell at the same time. You might want to use mice, and the neighbours may think you've gone mad, but it could be cheap fun (especially if you used a home made battery ).

You saw that Flying Squirrel vid, ya? Don't give Del any ideas.

Genius...

Place a ruler on a wall/target 10m away and measure how far the arrow drops.

It is the cheapest way-all you need is a ruler, the bow and some way to shoot the arrow reasonably horizontal(or at least measure its angle). You could use a laser pointer, a weight on a string + 2$ plastic protractor. It would work but resolution would be dodgy. You would have to repeat several times because there woul be a lot of error.

Other than that make a simple inductive chronograph-thingy with two coils, a micro, etc.

Inside your garage, filmed with the arrow visible against a brick wall (or a painted ruler scale). Camera frame rate checked separately by filming the second hand of a large clock. Probably the cheapest method if you have the camera...

You mean something like this?

This is a method I've seen used in Mythbusters. The alternating dark and light strips are a known thickness (a foot perhaps?). If the camera's frame-per-second setting can be varied, or known at least, then determining the speed should be simple.

I think a good quality camera would be needed though. One with a high frame-per-second capability.

regards,

Vulcan

Hello Vulcan,

Yes, that's it.

Many mass-market digital cameras offer 30 frames per second. Dedicated movie cameras usually offer options for higher frame rates.

Best regards,

dovy

Good plan -- camera, that is.

I made a 4 strobelight flash / camera system for Dunlop years ago so that they could measure golf ball spin rate as well as compression and velocity off the club head.

I used a 1 MHz oscillator and divided it down to 1 kHz and set off a sequence of four independent strobes to get film exposures exactly (close, anyway) 1 mS apart in time.

It was then that Dunlop advertised that they had a higher spin rate than Titlest. I even made one for their plant in England (for some reason, I think it was/is in Manchester).

I used an optical sensor to detect the golf shaft going by, experimented with various delays before catching the golf ball on film as it was being struck or just after being struck. To get the delay timing correct, I used a Polaroid camera with the shutter opened when their "Iron Byron" was fired. The picture quality was sufficient for the purpose. Thereafter, I used a Nikon with an electronic shutter which could be opened in "bulb" mode and then closed immediately after the fourth strobe.

Del, I know your a cheap bastard, frugal minded chap, but for the $100, making one could cost you even more, (and might not work or be way off).

http://www.opticsplanet.net/sport-sensors-arrowspeed-radarchron-arrow-archery-radar--velocity-sensor.html?productid=sport-sensors-arrowspeed-radarchron-arrow-archery-radar--velocity-sensor&channelid=BIZRA

Aw shucks, they're not that expensive! Here's one for £55: Chronograph

I made two chronographs for air guns using photo transistors and start-stop electronic timers for very little money ($25??) years ago. Had to calculate velocity from time difference between two points, but what the heck; it was cheap.

If you're accurate enough, you could use the same method at least one arrow length in front of the bow and another sensor any appreciable distance beyond that.

How many years ? As far as I know, a few things are costing approx 100 times they used to cost in my childhood. (and that includes Cat's Eye )

But I liked the idea of the audio recording I don't know why didn't cat_ch and latch onto it ?

Get two audio signals, once as you release the arrow from string and the other as it hits the garage door (assuming it is there- else you may hit kris outside) and it is easy to find the time between the two sounds on your PC

I would have preferred my suggestion - which obviously del didn't like - a scream could have been a better Cat_chable signal.

Don't recall the part numbers, but I used a barebones stopwatch IC with an LCD display, a LM7400 NAND gate for the phototransistor inputs. The stopwatch IC had a built-in 1kHz oscillator and LCD readout was in 1000ths of a second. I probably got the parts from Digi-Key or some other place like it. (I remember when Digi-Key's catalog was only a few pages . . .)

Sportsmansguide.com, in the US, has one for $79. I don't know if they ship to the UK.

FedEx ships worldwide, but international shipping is expensive and could eat up any savings over buying locally.

I remember seeing in an electronics hobby magazine years ago, a DIY project for a baseball timer. It had a wood frame holding 2 vertical strips of tin foil connected to a timer circuit, and spaced a foot apart. I didn't read the article because I wasn't interested, but I remember the cool illustration of the setup. I guess when the ball broke the first strip, that started the timer, and the second strip stopped it.

You should have enough wood left over from some of your bowmaking or sculpture projects for the frame, foil is cheap, IC555 timers are cheap. Don't know about the other components or what would be required, but I guess a relay or two might be in there somewhere.

Get two sheets of paper and glue sheets of aluminium foil to them then cut out the waste foil with two Stanley blades taped together with a separator in between:-

Depends how often you want to do it I suppose. You could repair and re-use sheets made like this a few times.

Cheers,
If I'm going to be bothered to make one* () I'll go for rugged and re-usable.
Mind, the strips would be good for a quick one off lashup.
Del

*It is my intention .... at the moment (terms and conditions apply)

Del,

It's hard to believe that you don't know where to find one to borrow!!! Frugal you.

Our local bowhunting club has some fanatical individuals who have built their own, similar to the one shown in the link "chronograph" earlier provided.

Calibration of the units was dependant on accuracy of the spacing of the "V" bows (which are attached to strain gauges and triggered by the deflected air as the arrow passes through.) linked to a simple electronic stopwatch with 0.001 second resolution.

So, get the two strain gauges (cheap electronic kitchen scales might do the trick with "air movement sensors" firmly attached to the plates, but be cautious when Mrs cat finds what you are doing.) and your osciloscope. Get the signal from each of the scales and "trigger" on the first and observe the second trace. From there I'm sure you can do the maths.

For our guys, it was as simple as fire the arrow, measure "t" and then speed was 1/t m/second when the bows were 1m apart.

Some of the guys used to "calibrate" their arrows by trimming the flights and shaving the tips so that all 12 arrows in a set had the same speed out of the bow.

We use the chronoghraphs inside the garage, inside the clubhouse or on the open range on still times of the day. We've had three inside ranges over the years, girl guides clubhouse, retirement home meeting hall and a small pavilion at the local showground. Our outdoor range includes 4 x 2km long walk 20 target ranges (Like playing 20 hole golf) on around 100 Acres (40Ha). Our range masters (fanatical bowhunters) also arrange 3D target days on the range, or even on some of our properties.

Projectile motion ? ignoring wind resistance (drag) or may be correcting for it ?

Cheers, You're a good shot! (at least in your illustration)
I've got some phototransistors on the way, but if that doesn't work I could try some BIG coils...the arrow points are steel, so I could magnetize one.

I'd probably need a 20" dia coil to make sure I didn't hit the coil (shooting at close range with a bow can be problematic as the arrow is 'snaking' as it leaves the bow.
This is due to it having to bend around the bow (the archer's paradox).
I posted a thread on it a while back.

Del

Cheers, Del,

the "coils" can be larger loops with a couple of turns.

(My son also deals with archery and he must be somewhere here in CR4. Maybe later he will also tell his idea)

You can avoid magnetizing or altering the arrow in any way by operating the coils as components of a tank circuit - like the coil in a metal detector. The arrow point changes the inductance - and therefore the tank's resonant frequency - as it passes through. The two coils may be connected in series to form a single inductance where each coil is simply a separate set of widely-spaced windings. Because they will be fairly close together (in terms of the ratio of distance vs coil radius) they will inductively couple. This would be a problem if each coil were part of a separate tank circuit, as each tank would very likely interfere with the other. But by combining them as part of a single tank, you need only look for two shifts in the resonant frequency as the arrow point passes through.

Combining Qqberci at #40 and #42 and europium at #45 with your original plan to use a DSO (digital storage oscilloscope): you can knock up a working system in no time. Scopes nowadays are unbelievably good at triggering on pulse widths outside certain tolerances, and you can capture huge waveforms. Once you've captured a "shot" you should be easily able to figure out which events caused which perturbations of the frequency. Now to productionise it you'll need to add: a frequency to voltage converter; A to D; a small processor with display, and, a calibration routine. You might need to re-calibrate when you change the coils because someone has shot through them at the other end of the range (if you wanted to say figure out how much the arrow slowed down in flight).

The scope will help in the R&D, but I want to end up with a nice portable which I can the lose in the garage under all the junk.

I started writing software this afternoon (well cutting out the surplus stuff from existing software...and making a few hardware plans)

Del

Hello europium:

How are you?..............You are getting too many GA's in this thread!

But hell, here is another! Take care my friend. GA to you! You clever bug-er!

PS. Am sending this in safe mode, as my computer is f, f, fried, thats what I was going to say!

Getting a little laptop to help me mend the main doodad.

Del, the commercial ones do not use antennas, they are almost all optical. The "antenna" you are seeing are merely skyscreens that give a bright diffuse monocolor background light to improve contrast for the sensor. they have to be replaced periodically as they age and discolor or get acidentally shot off.....=D when you use them indoors you have to put a lamp on them because indoor ranges are notoriously dark (hard to keep the light fixtures working when they keep getting shot up.)

I know you are pretty handy with a soldering iron, and even know which end gets hot, but I think you might have a hard time building one for the cost of buying one off the shelf.

The radar guns are also sold in sporting goods stores (well, at least here in the states.) for clocking baseball/softball pitches. but they don't go much above 100 mph. That might be good enough for a bow (probably not a crossbow, or a high performance longbow though), but it won't work for a bullet which is what chronographs were originally intended for.

Here is a couple links for you to buy one.

Midway USA

Cabelas

This one is metric and is on clearance for $58.72 US

I guess there isn't much demand for a chony that reads out in meters per second here in the land of barbarians.

This one is radar based specifically designed for archery (but it requires an optic mount which your home grown bows probably don't have so you'd have to make some kind of clamp on arrangement.) and it maxes out at 450 ft/sec.

Here is a pitching speed gun, it's range is 6-110 mph. That might be a bit slow for your purposes.

Cheers, I may just buy one.
Some of the fun is just the challenge of building one especially as things are a tad quiet at work at the moment and I can call it 'R&D*', it's nice to dabble with analogue too as most of my stuff is just writing new software for our existing boards.

Ta for the 'antenna' info.
BTW, good point it will need to over 100mph, I'm sure my longbow will go over.

Del
* Investigation of optical methods of fluid level sensing .
A bit of play R&D often has knock on benefits, if only stopping my brain stagnating.

Agreed! Making is certainly more fun than buying! But justifying making on the basis of cost is probably not going to fly.

Things have been slow at work here as well. So slow in fact that I have been asked to seek other employment.....

Hello Del,

How are you?....................Try this company if you are looking to buy?

http://www.balluff.com/Balluff/gb/ProductsChannel/Overview/en-gb/Photoelectric+Sensors.htm

You could perhaps have two sensors, a metre apart and as close as is practicable to the release point. Use an arrow with no point and glue a quill maybe painted black so it can be seen? Thats it really. I say a quill because they are light, but you could use a matchstick? Simple maths and the speed in metres per second etc is yours.

Are you testing different bows for strength Del?

Good luck and take care...........

Hi, the design is well on the way to fruition thanks.
The purpose of it is to compare and tune bow designs, types of wood etc.
The draw weight of the bow isn't necessarilly related to the arrow velocity (or range). E.G In one of my books it tells how they took a poorly made very long Ironwood bow with a 90lb draw weight, they shortened it by a few inches re-tillered it (re-shaped the limbs) down to about 70lb and it shot further.

There are plenty of variables the material, cross section, length, re-curve, draw length, bracing height (the distance between string and bow at rest).
It will be a tool and a toy really.
Not to mention the arrow design for maximum velocity or maximum arrow energy.

There's endless potential for tinkering and drawing graphs.

Del

I've got another brilliant idea......lie down on a suitable bench and fire upwards......using a stop watch.......You may need to get this one right first time

Shoot the arrow into something. Put a mike at the bow and one at the something. Run the audio to your oscope. Read the time between the poing and the splat.

I'm not too sure how to do it, but I was thinking you could use a laser pointer and some front surface mirrors and a laser detector to time passage of the arrow as it breaks the laser beam?

Yeah, if I zig zagged the beam back and forth to form a reasonable area the arrow could break it.
Del

Here's an idea: Rig up two of those laser scanners they use in grocery stores and stick UPC stickers on your arrows. As the arrows pass by the terminal reads: Deluxe Del-the-Cat Arrow. Price: Speed: 172.3 fps plus tax. Subtotal: 835.6 fps.